Method of protecting broadcast frame, terminal authenticating broadcast frame, and access point broadcasting broadcast frame

• US 20080159535A1
• Filed: 09/12/2007
• Published: 07/03/2008
• Est. Priority Date: 12/27/2006
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Fomin, Alexey, Bezzateev, Sergei, Kim, Eun Ah, Jung, Tae-Chul, Yi, Jeong Hyun, Stepanov, Mikhail, Linsky, Evgeny
• Granted Patent: US 8,270,607 B2
• Time in Patent Office: Days
• US Class Current: 380/258
• CPC Class Codes: H04L 2209/601 Broadcast encryption
• CPC Class Codes: H04L 9/14 using a plurality of keys or algorithms
• CPC Class Codes: H04L 9/3239 involving non-keyed hash functions, e.g. modification detection codes [MDCs], MD5, SHA or RIPEMD
• CPC Class Codes: H04L 9/50 using hash chains, e.g. blockchains or hash trees
• CPC Class Codes: H04W 12/06 Authentication
• CPC Class Codes: H04W 84/12 WLAN [Wireless Local Area Networks]

Abstract

A method of protecting a broadcast frame, the method comprising broadcasting a beacon and a maintenance beacon frame (MBF) from an access point (AP) to a plurality of terminals during a maintenance beacon waiting period (MBWP); and broadcasting broadcast management frames (BMFs) from the AP to the plurality of terminals during a broadcast management frame waiting period (BMFWP), wherein the MBF comprises a BMFs message integrity code (MIC) field including a BMFs MIC calculated from concatenated BMFs to be sent in a current beacon interval.

Claims

1. A method of protecting a broadcast frame, the method comprising the steps of:

broadcasting a beacon and a maintenance beacon frame (MBF) from an access point (AP) to a plurality of terminals during a maintenance beacon waiting period (MBWP); and

broadcasting broadcast management frames (BMFs) from the AP to the plurality of terminals during a broadcast management frame waiting period (BMFWP),

wherein the MBF comprises a BMFs message integrity code (MIC) field including a BMFs MIC calculated from concatenated BMFs to be sent in a current beacon interval.

2. The method of claim 1, wherein the broadcasting of the beacon and the MBF comprises:

creating the MBF including a previous key field, a beacon MIC field, a BMFs number field indicating a number of BMFs to be sent in the current beacon interval, and the BMFs MIC field; and

broadcasting the beacon and the MBF to the plurality of terminals.

3. The method of claim 2, wherein the creating comprises:

including a previous key from a previous beacon interval in the previous key field;

calculating the beacon MIC using a current key for the current beacon interval, and including the beacon MIC in the beacon MIC field;

including the number of BMFs to be sent in the current beacon interval in the BMFs number field; and

including the BMFs MIC, calculated from the concatenation of the BMFs using the current key, in the BMFs MIC field when the number of BMFs is different from 0.

4. The method of protecting a broadcast frame at the plurality of terminals of claim 1, further comprising the step of:

saving a time when the beacon was received by using a security timer; and

saving the received beacon into a buffer.

5. The method of protecting a broadcast frame at the plurality of terminals of claim 1, further comprising:

checking, using a security timer, whether the MBF was received during the MBWP;

checking, using an initial group temporal key (IGTK), whether the MIC of the MBF is valid; and

saving the received MBF into a buffer.

6. The method of protecting a broadcast frame at the plurality of terminals of claim 5, further comprising the steps of:

checking whether a time synchronization was performed during a previous beacon interval;

when the time synchronization was not performed during the previous beacon interval, extracting a previous key of a previous key field of the MBF, and checking whether the previous key belongs to a hash chain and corresponds to the previous beacon interval; and

when the time synchronization was performed during the previous beacon interval, performing the time synchronization.

7. The method of protecting a broadcast frame at the plurality of terminals of claim 1, further comprising the steps of:

checking, using a security timer, whether the BMF was received during the BMFWP;

checking, using an IGTK, whether the BMFs MIC is valid;

increasing the number of the received BMFs;

comparing the number of the received BMFs with a value included in a BMFs number field of the MBF saved in a buffer; and

authenticating the BMF by using the BMFs MIC when the number of the received BMFs is equal to the value.

8. The method of claim 7, wherein the authenticating comprises:

extracting a current key from a key identification (ID) field included in a management MIC information element (MMIE) field of a first BMF;

checking whether the extracted current key belongs to a hash chain and corresponds to a previous beacon interval;

checking whether a first MIC, which is the MIC included in the MBF, is valid by using the current key when the extracted current key belongs to the hash chain and corresponds to the previous beacon interval; and

checking whether a second MIC, calculated on the concatenation of received BMFs, is equal to the first MIC.

9. The method of claim 1, further comprising the steps of:

calculating a plurality of keys which is used at every beacon interval in the AP by using a hash chain in accordance with the equation K_i-1=Truncate-128(SHA-256(K_i)), where K₀, which is referred to as an IGTK, is used as a public key, Truncate-128(.) returns the left-most 128 bits of the public key'"'"'s argument, and SHA-256(.) returns the SHA-256 digest of the public key'"'"'s argument,

wherein a key validity of the plurality of keys is verified in accordance with the equation K_j=(Truncate-128(SHA-256(K_i)))^i-j, where j is a number of a last received key from a key chain and (.)^i-j refers to i-j recursive executions of a function in brackets.

10. A computer-readable recording medium storing a program for implementing a method of protecting a broadcast frame, comprising:

broadcasting a beacon and an MBF from an AP to a plurality of terminals during an MBWP; and

broadcasting BMFs from the AP to the plurality of terminals during a BMFWP,

wherein the MBF comprises a BMFs MIC field including a BMFs MIC calculated from concatenated BMFs to be sent in a current beacon interval.

11. A terminal which authenticates a broadcast frame, the terminal comprising:

a security timer for checking a receipt time of a beacon, an MBF, and BMFs which are received from an AP for a time synchronization and a validity check;

an MBF processing unit for verifying a validity of the MBF received from the AP, and storing the MBF;

a BMF authentication unit for verifying a validity of the BMFs received from the AP, and authenticating the BMFs by using the MBF,

wherein the terminal receives the beacon and the MBF during an MBWP of a beacon interval, and receives the BMFs during a BMFWP of the beacon interval.

12. The terminal of claim 11, wherein the MBF processing unit comprises:

an MBF receipt period check unit for checking whether the MBF was received during the MBWP by using the security timer;

an MBF MIC check unit for checking an MIC of the MBF by using an IGTK; and

a buffer for storing an MBF where the MIC of the MBF is checked.

13. The terminal of claim 12, further comprising:

a time synchronization check unit for checking whether the time synchronization was performed during a previous beacon interval of the beacon interval;

a key check unit for extracting a previous key of a previous key field of the MBF, and checking whether the previous key belongs to a hash chain, and corresponds to the previous beacon interval when it has not been checked whether the time synchronization was performed; and

a time synchronization performing unit for performing the time synchronization when it has been checked whether the time synchronization was performed.

14. The terminal of claim 11, wherein the BMF authentication unit comprises:

a BMF receipt period check unit for checking whether the BMF was received during the BMFWP by using the security timer;

a BMF MIC check unit for checking whether a BMFs MIC is valid by using an IGTK;

a number increase unit for increasing a number of the received BMFs;

a comparison unit for comparing the number of the received BMFs with a value included in a BMFs number field of the MBF saved in a buffer; and

an authentication unit for authenticating the BMF by using the BMFs MIC when the number of the received BMFs is equal to the value.

15. The terminal of claim 14, wherein the authentication unit comprises:

a key extraction unit for extracting a current key from a key ID field included in an MMIE field of a first BMF;

a key check unit for checking whether the extracted current key belongs to a hash chain and corresponds to a previous beacon interval;

a first MIC check unit for checking whether a first MIC, which is the MIC included in the MBF, is valid by using the current key when it has been checked whether the extracted current key belongs to the hash chain and corresponds to the previous beacon interval; and

a MIC check unit for checking whether a second MIC, calculated from a concatenation of the received BMFs, is equal to the first MIC.

16. The terminal of claim 11, wherein the AP calculates a plurality of keys which is used at every beacon interval in accordance with the equation K_i-1=Truncate-128(SHA-256(K_i)), where K₀, which is referred to as an IGTK, is used as a public key, Truncate-128(.) returns the left-most 128 bits of its argument, and SHA-256(.) returns the SHA-256 digest of its argument,

and the terminal further comprises a key validity verification unit for verifying a key validity of the plurality of keys in accordance with the equation K_j=(Truncate-128(SHA-256(K_i)))^i-j, where j is a number of a last received key from a key chain and (.)^i-j refers to i-j recursive executions of a function in brackets.

17. An AP broadcasting a broadcast frame, the AP comprising:

an MBF creation unit for creating an MBF including a previous key field, a beacon MIC field, a BMFs number field indicating the number of BMFs to be sent in a current beacon interval, and a BMFs MIC field;

a first broadcast unit for broadcasting an MBF from an AP to a plurality of terminals during an MBWP;

a second broadcast unit for broadcasting BMFs to the plurality of terminals during a BMFWP,

wherein the MBF comprises the BMFs MIC field including a BMFs MIC calculated from concatenated BMFs to be sent in the current beacon interval.

18. The terminal of claim 17, wherein the MBF creation unit comprises:

a creation unit for creating the MBF including a plurality of fields;

a previous key including unit for including a previous key from a previous beacon interval in the previous key field;

a beacon MIC including unit for calculating a beacon MIC using a current key for the current beacon interval, and including the beacon MIC in the beacon MIC field;

a BMF number including unit for including the number of BMFs to be sent in the current beacon interval in the BMFs number field; and

an MIC including unit for including the BMFs MIC, calculated from the concatenation of the BMFs using the current key, in the BMFs MIC field when the number of BMFs is different from 0.